This invention relates to hybrid propulsion systems for nonstationary applications, such as vehicle drive, farm-machine drive, boats, etc., and more particularly to the adaptation of a hybrid flywheel/compressed-fluid propulsion system as a power drive for nonstationary applications. Compressed-fluids, such as compressed-air, have been used as an energy-storage medium for driving energy converters, such as turbines, which act as process plant drivers for many decades. Although many successful stationary applications of a compressed-air turbine can be found in various industries, very few nonstationary applications of the same have been reported in the literature. This is because the limited energy-storage capacity of a compressed-fluid that results in a restricted operating range makes its application impractical or economically infeasible.
Significant advances have been made recently in the structural materials and designs of high-pressure vessels. High-pressure compressors have also improved greatly over the years. Now, it is practical to generate and store a compressed-fluid at pressures over 30,000 pounds per square inch. Today, high-pressure vessels and compressors are lighter and more compact than they were twenty years ago due to the lighter and better structural materials and the advanced designs used. But, this will still result in a limited supply of energy of a compressed-fluid when used in nonstationary applications, such as vehicle drive. Therefore, every practical step must be taken to maximize the use of this limited energy supply if it is to be viable for nonstationary applications in this time frame.
In spite of the limited supply of energy, a compressed-fluid is an attractive energy-storage medium especially when compressed-air is used for vehicle drive since it has several advantages over other available energy-storage media. These advantages are: (1) truly nonpolluting; (2) using the unlimited supply of air; (3) having high energy efficiencies; (4) the braking energy can be recovered substantially; (5) fewer moving parts requiring little maintenance; (6) long service-life; (7) quick-recharging, etc.
While vehicle range may be improved by using lighter materials and improved designs it will still be governed by the energy stored in the compressed-fluid as well as the way the vehicle is used. The range of a vehicle driven by a compressed-fluid propulsion system will be very much dependent on many factors which fall into two major categories. The first is concerned with the compressed-fluid itself and includes such factors as the initial pressure, temperature, and volume. The second is concerned with the way in which the vehicle is operated and includes the total weight, the vehicles speed, the number of starts and stops per driving cycle, the acceleration, the wind conditions, the road-surface conditions, and the variation from a level route. In general, increased performance in these operational categories requires higher fluid-pressures and volumetric flow-rates from compressed-fluid, resulting in less total energy being available for traveling.
According to the results of studies made by this inventor, a key to improving vehicle range is to remove the requirement for peak powers from the compressed-fluid propulsion system in the operational categories described above. The results also indicated that once the vehicle has reached its maximum speed, the power requirement for maintaining its speed is approximately one fourth of the peak value. At this point in the driving cycle, if the vehicle velocity is held constant, the power requirement of the vehicle is approximately equal to the losses due to the expander, drive trains, aerodynamic drag, and the rolling resistance of the tires. My above studies have concluded that the peak power requirements during vehicle acceleration greatly reduce the available energy supply of the compressed-fluid for traveling. Therefore, it is essential to provide a system which can prevent these peak power drains in the compressed-fluid propulsion system used for vehicle drive. My studies further indicated that a second key to improving vehicle range is to recover the braking energy when the vehicle decelerates. Without the use of a recovery system, the kinetic energy generated through a propulsion system, such as a compressed-air turbine, will be dissipated partly in the frictional braking system as heat and partly in the rolling resistance and vehicle drag as it decelerates.
The main object of this invention is to provide a viable compressed-fluid propulsion system, such as compressed-air, for nonstationary applications, especially for vehicle drive by combining with a secondary power source capable of reducing peak powers drained in the compressed-fluid propulsion system during the acceleration cycle and recovering the braking energy during the deceleration cycle.
Other important objects of this invention are: (1) to provide a truly nonpolluting propulsion system for nonstationary applications, especailly vehicle drive; (2) to provide a propulsion system for nonstationary applications, especially vehicle drive, which utilizes power-storage media capable of quick-recharging; (3) to provide a propulsion system for nonstationary applications, especially vehicle drive, which contains a regenerating system for recovering the braking energy and which operates with high energy efficiencies; (4) to provide a propulsion system for nonstationary applications, especially vehicle drive, which requires little maintenance and which has a long service life, etc.